The fault-finding in all these cases rests on observation, true as far as it goes; but the total absence of genial relations with the entirety of the phenomenon discussed, the clutching at some paltry mechanical aspect of it that lends itself to reasoned proof by _a_ plus _b_, and the practical denial of everything that only appeals to vaguer sentiment, show a mind so oddly limited to ratiocinative and explicit processes, and so wedded to the superficial and flagrantly _insufficient_, that one begins to wonder whether in the philosophic and scientific spheres the same mind can have wrought out results of extraordinary value. Both "yes" and "no" are here the answer. Every one who writes books or articles knows how he must flounder until he hits upon the proper opening. Once the right beginning found, everything follows easily and in due order. If a man, however narrow, strikes even by accident, into one of these fertile openings, and pertinaciously follows the lead, he is almost sure to meet truth on his path. Some thoughts act almost like mechanical centres of crystallization; facts cluster of themselves about them. Such a thought was that of the gradual growth of all things, by natural processes, out of natural antecedents. Until the middle of the nineteenth century no one had grasped it _wholesale_; and the thinker who did so earliest was bound to make discoveries just in proportion to the exclusiveness of his interest in the principle. He who had the keenest eye for instances and illustrations, and was least divertible by casual side-curiosity, would score the quickest triumph.